Recently, an LED (Light Emitting Diode) has attracted attention as a light-emitting element with high brightness and low power consumption which can be mass-produced. LEDs have been widely used for general illuminations, a light source of an electronic display board and a backlight of a mobile phone, a computer, a television, and the like.
A substrate itself for mounting such a light-emitting element is required to have high reflectance to enhance heat dissipation performance.
In response to this requirement, Patent Literature 1 discloses that light reflectance at a wavelength of 400 to 740 nm is in the range of 90% to 93%, in that a high-reflectance white ceramics substrate for a semiconductor light-emitting element is formed of aluminum oxide and a glassy component to have porosity of 5%, the content of aluminum oxide is in the range of 75 to 85 wt %, silica, calcium, magnesium, and barium are contained as the glassy component, and the average crystal grain size of aluminum oxide is 0.5 μm or less.